1. Field of the Invention
The present invention relates to an apparatus for increasing a cell capacity in a mobile communication base station and a method for controlling the same, and more particularly to an apparatus for increasing a cell capacity in a mobile communication system using an adaptive sectorization and a method for controlling the same, wherein the adaptive sectorization is applied to a mobile communication base station to improve an inter-sector traffic imbalance resulting from a user distribution in a cell so as to increase the cell capacity.
2. Description of the Related Art
A smart antenna technique and adaptive sectorization have recently been developed to be applied to a mobile communication base station system to increase a cell capacity. The smart antenna technique is superior in performance to the adaptive sectorization.
However, in order to apply the smart antenna technique to a base station, a modem and transceiver must be redesigned for application of an adaptive beam former, and the transceiver must be increased in capacity to process signals on an extending antenna path. The smart antenna technique necessitates a variety of additional functions, such as a diversity function, a steering function, a tilting function, a cell configuration change function based on transmission/reception power control, etc., besides functions essential to an increase in base station capacity, thereby making the base station very complicated in construction, and considerably hard to design and implement, resulting in difficulties in operating the base station.
Accordingly, in the mobile communication field, the smart antenna technique is not applied to the base station due to difficulties in implementing the base station, although it is superior in performance to the adaptive sectorization.
Meanwhile, the adaptive sectorization is a technique for controlling a sector size adaptively to a given environment using a multi-array antenna. This technique is applicable to cellular mobile communication base stations of a code division multiple access (CDMA) system, a time division multiple access (TDMA) system and a wireless local loop (WLL) system.
Effects of a capacity increase by the adaptive sectorization will hereinafter be described in more detail with reference to an example. Assuming that the total capacity of one sector is N, the capacity of a cell composed of three sectors is 3N. However, provided that the cell has such a nonuniform user distribution that 2N users are concentrated in a specific one of the three sectors and N users are spread over the remaining two sectors, the current capacity of the cell will become 2N because the capacity of one sector is no more than N although the total capacity of the cell is 3N. In this case, if the adaptive sectorization is used to reduce the size of the sector concentrated with 2N users to N and allocate 2N users to the other two sectors, the cell can provide services at its original maximum capacity, in that it has a capacity of 3N, owing to the sector size adjustment, although the user distribution is subject to no variation. However, in order to apply the adaptive sectorization to a mobile communication system, there is a need to modify internal constituent elements and the structure of the system, which leads to technical difficulties causing difficulties in use.
On the other hand, a conventional mobile communication 3-sector base station comprises, as shown in FIG. 1, a transceiver 10 including a radio frequency (referred to hereinafter as RF) controller 11. The transceiver 10 acts to perform functions for transmission/reception of data to/from a base station controller, such as a data digital/analog (D/A) conversion function, an up/down conversion function, a modulation/demodulation function, etc. The conventional mobile communication 3-sector base station further comprises a power amplifier 20 for receiving and amplifying an RF signal from the transceiver 10, a front-end unit (FEU) 30 for performing a noise removal function upon transmission and reception of RF signals, and a plurality of diversity antenna modules 40, each having two antennas for a corresponding sector. The conventional mobile communication 3-sector base station has a fixed 3-sector cell structure as shown in FIG. 2.
However, the above-mentioned conventional fixed 3-sector base station has a disadvantage in that the capacity of a cell is reduced due to an inter-sector traffic imbalance resulting from a user distribution in the cell, causing a significant reduction in the quality of speech.